A position sensor is a device that can detect the presence and location of a touch, by a user's finger or by an object, such as a stylus, for example, within a display area of the position sensor display screen. In a touch sensitive display application, the position sensor enables a user to interact directly with what is displayed on the screen, rather than indirectly with a mouse or touchpad. Position sensors can be attached to or provided as part of computers, personal digital assistants (PDA), satellite navigation devices, mobile telephones, portable media players, portable game consoles, public information kiosks, and point of sale systems etc. Position sensors have also been used as control panels on various appliances.
There are a number of different types of position sensors/touch screens, such as resistive touch screens, surface acoustic wave touch screens, capacitive touch screens etc. A capacitive touch screen, for example, may include an insulator, coated with a transparent conductor in a particular pattern. When an object, such as a user's finger or a stylus, touches or is provided in close proximity to the surface of the screen there is a change in capacitance. This change in capacitance is sent to a controller for processing to determine the position of the touch.
An array of drive (in one example X) electrodes or lines and sense (in this example Y) electrodes or lines, of conductive material, can be used to form a touch screen having a plurality of nodes. A node is formed at each intersection of X and Y electrodes. Although referred to as an intersection, the electrodes cross but do not make electrical contact. Instead, the sense electrodes are capacitively coupled with the drive electrodes at the intersection nodes. Applying a voltage across the array of electrodes creates a grid of capacitors. When an object touches (contacts or comes in close proximity to) the surface of the screen, the capacitance change at every individual point on the grid can be measured to determine the location or position of the touch.
In recent years, it has become desirable for touch sensitive position sensors to be used in large screens. As touch screen size grows, the number of capacitive sensing nodes contained in a touch screen increases. To measure capacitance at more nodes on a screen requires increased measurement device capacity, either in the form of more complex measurement devices or chips or in the form of more measurement devices, to handle all the nodes of the larger screen size. A screen of four times the node count as could be handled by a particular size/capacity of measurement chip, for example, might use four measurement chips each measuring signals for a quarter of the touch screen. If the capacity of each measurement chip stays the same, large screens may require a very large number of measurement chips.